Center Custom Menu in 2010 Theme

Hello All,
I am trying to center the custom menu for my WordPress site using the 2010 theme (the website is Seattle7Writers.org) Previously, I was able to center the default menu before using this custom CSS:

.menu {
text-align:center;
}

.menu ul {
display:inline-block;
}

However, now that I am using a custom menu (which I called "menu alt") it does not appear to work. Would anyone know how I would have to alter the CSS to target the new custom menu? I have tried a number of changes, but none seem to work. Thank you in advance for any help you can provide.

a) It has to do with setting it relative, using a "left" value of half the div width and then also declaring a -50% left margin. I've used it before, but failed to record it and when I went back and searched for it, this time I could not get it to work.